1. Field of the Invention
This invention relates to a trigger in an active database management system and, more particularly, to a trigger for automatically starting an extract process in response to the updating of a data repository by an update process.
2. Description of the Related Art
Conventional database management systems are "passive" in the sense that they only manipulate data in response to explicit requests from applications. Recently, so-called "active" database management systems have been developed that respond automatically to specified events without active user intervention. The operation of such active database management systems may be specified in the form of event-condition-action (ECA) rules, so called because upon the occurrence of a specified event, a specified condition is evaluated and, if the condition is satisfied, the specified action is executed. Active database management systems and ECA rules are discussed in such references as the following (incorporated by reference herein):
D. R. McCarthy and U. Dayal, "The Architecture of an Active Data Base Management System", SIGMOD Record, vol. 18, no. 2, June 1989, pp. 215-224.
U. Dayal, M. Hsu and R. Ladin, "Organizing Long-Running Activities with Triggers and Transactions", SIGMOD Record, vol. 19, no. 2, June 1990, pp. 204-214.
O. Diaz, N. Paton and P. Gray, "Rule Management in Object Oriented Databases: A Uniform Approach", Proceedings of the 17th International Conference on Very Large Data Bases, Barcelona, Sept. 1991, pp. 317-326.
N. Gehani and H. V. Jagadish, "Ode as an Active Database: Constraints and Triggers", Proceedings of the 17th International Conference on Very Large Data Bases, Barcelona, Sept. 1991, pp. 327-336.
A large number of applications can be structured as a set of processes that update data in a database (update processes) and another set of processes that require the updated data as input (extract processes). ECA rules (or triggers, as they are commonly called) may be integrated into such systems to automate the starting of the extract processes. To be truly useful in such applications, ECA rule languages should achieve several objectives. They should move data collection programming as much as possible out of the extract processes and into the triggers. They should also allow for the coding of data extraction programs independently from programs updating a repository. Needless to say, they should perform efficiently.